It is known that perfluorinated organic compounds having functional moieties are useful intermediates for manufacturing a variety of valuable chemical compounds, such as notably perfluoromonomers (e.g. perfluorovinylethers) and fluorosurfactants.
A convenient approach for the synthesis of functional perfluorinated compounds involves fluorination of hydrogen-containing alcohols, the hydroxyl moiety being possibly derivatized to yield the target functional moiety. However, hydrocarbons containing functional hydroxyl moieties are generally unstable under conditions of traditional fluorination processes, typically comprising a first step carried out at low temperature and high dilution, followed by a further step involving high temperatures and concentrations of fluorine, as required in order to reach satisfactory yields of the perfluorinated compound. Under these conditions, it is generally understood that compounds having hydroxyl groups decompose, with simultaneous release of HF and COF2, and subsequent formation of corresponding non-functional perfluorocompound having one less carbon atom than the starting hydroxyl-containing compound.
In order to overcome this problem, EP 1164122 A (ASAHI GLASS CO LTD) Dec. 19, 2001 discloses a process for producing fluorinated compounds wherein a primary hydrogenated alcohol is first converted into the corresponding ester, generally a partially fluorinated ester, as obtained by reaction with a (per)fluorinated acyl fluoride, and then subjected to fluorination in liquid phase. The so-obtained perfluorinated ester can be then thermally cleaved or decomposed with suitable agents, to obtain perfluorinated acyl fluoride corresponding to the starting hydrogenated alcohol.
Similarly, U.S. Pat. No. 7,053,237 (ASAHI GLASS CO LTD) Nov. 24, 2005 discloses a process for producing a fluorinated ester, wherein a primary hydrogenated alcohol is protected via transesterification and then subjected to fluorination in liquid phase.
However, the above described processes have the drawback that, in order to prevent decomposition of the reagents due to the reaction exothermicity, it may be necessary to operate under diluted concentrations both of fluorine and of the hydrogen-containing alcohol. Furthermore, to obtain a fully fluorinated product, a large excess of fluorine over the stoichiometrically required quantity, is needed. These conditions might negatively affect the reaction rate, yielding low productivity of the overall process.
Furthermore, as already mentioned, in order to reduce fluorine consumption, protection of the alcohol moiety as an ester is generally performed using suitable perfluorinated carboxylic acid derivatives, generally acyl fluorides, whose availability might be costly and induce further steps for appropriate separation, recovery and reuse.
As an alternative to this pathway, hydrogen-containing alcohols have been protected under the form of fluoroformates before undergoing fluorination.
Thus, U.S. Pat. No. 3,900,372 (PHILLIPS PETROLEUM) Aug. 19, 1975 discloses a process for the production of perfluorinated organic compounds from hydrogen-containing alcohols. The process comprises protection of the hydroxyl moieties of the hydrogen-containing alcohol by reaction with carbonyl fluoride to yield corresponding hydrogen-containing fluoroformates. Said fluoroformates are then subjected to an electrochemical fluorination step, and the resulting perfluorinated counterparts still possessing the fluoroformate functionality are subsequently cleaved by the action of fluoride ions under reacting conditions for yielding corresponding acyl fluorides. Further, it is known that perfluorinated fluoroformates can be converted into fluoroacyl fluorides with loss of carbonyl fluoride, easy to separate and recover.
Nevertheless, electrochemical fluorination is a burdensome and energy-consuming procedure, which is generally less economically and industrially acceptable than fluorination with elemental fluorine, particularly when a single compound has to be obtained. Furthermore, yields in electrochemical fluorination are known to be mostly moderate or even poor, especially if high molecular weight compounds have to be fluorinated.
Attempts to fluorinate with molecular fluorine certain fluoroformates have been already disclosed in the art. In particular, GB 1226566 (MONTECATINI EDISON) Mar. 31, 1971 discloses a process for the preparation of certain perfluorinated polyethers wherein possible terminal groups of acidic nature, such as formate moiety, are eliminated. Conversion by severe heat treatment of a perfluorinated polyether having a fluoroformate terminal group into a fluoroacyl fluoride is also described.
There is thus still a need in the art for a process for producing perfluorinated compounds having a functional moiety from hydrogen-containing alcohols comprising a fluorination step that may be carried out under mild conditions and providing high yields.